The present invention relates to a method of producing a lamp having a coated layer such as a fluorescent lamp with a plural number of glass element tubes having openings at both ends and connected at the side of the openings to form a single discharge path, and more particularly to a method of producing a lamp in which an internal portion of a connecting portion cannot be seen and in which the connecting portion also emits light in the same manner as the other portions of the glass tube.
In recent years, linear glass element tubes having either two or four openings at each end have been connected in the vicinity of these openings to form so-called compact fluorescent lamps that form discharge paths that are bent into either an H-shape or a double H-shape.
The following are known as methods of producing such compact fluorescent lamps.
A fluorescent lamp having such a shape and structure is manufactured using technology such as that for "METHOD OF PRODUCING A LOW-PRESSURE MERCURY VAPOR DISCHARGE LAMP" as described in U.S. Pat. No. 4,324,447 (hereinafter cited as Wolf et al.).
As is clear from referral to Wolf et al., after several fluorescent tubes have been manufactured, had one end closed and a luminescent agent coated to their inner walls, the gas fusion method is used to introduce a gas flow via a discharge tube and at the same time fuse the glass element tubes so that an aperture is formed between adjacent tubes.
However, according to such a method, the gas tubes are fused after the luminescent layer has been formed and so it is easy for the luminescent substance to enter into the connecting portion and produce cracks. In addition, when the luminescent substance on the inside walls of the connecting portion is cleaned, it is difficult to do so unless the diameter of the connecting portion is large. This is because the particles of the luminescent substance are sized in the order of several microns in the case of a luminescent layer and so unless the diameter is made large, it is not possible to connect the tubes without removing the luminescent layer. Accordingly, it is possible to perform coating of a protective layer of aluminum or titanium particles that have particle diameters in the sub-micron order, and this creates a problem for the application of this method to fluorescent tubes of the type where a protective layer is provided. The following prior art has been proposed in order to overcome this problem.
(A) A method to form an opening for tube connection without causing cracks or breakages by attaching a phosphor-coating adherence preventing member in the vicinity of an open end of a glass element tube, and by removing the preventing member after application of a phosphor screen to the tube inner surface (refer to Japanese patent application Laid-Open Publication No. 62-287545 (1987)).
(B) A method to apply a phosphor-coating layer to the inside wall of a glass element tube and to form a luminescent layer by baking after drying, and then removing the phosphor coating layer on the glass tube in the vicinity of their open ends, sealing the tubes at these parts and also providing a through hole on the side of the tube so as to join the plural number of tubes (refer to Japanese Patent Application Laid-Open Publication No. 63-13233 (1988)).
(C) A method to form a phosphor coating layer in the same manner to the inside wall of a glass element tube, closing the openings with the luminescent layer still attached and then connecting the portions of the glass element tubes where they are to be connected (See Japanese patent application Laid-Open Publication No. 62-281229 (1987)).
However, there are the following problems with these conventional technologies.
With method (A) of J.P. No. 62-287545, it is necessary to have a coating prevention layer, and the labor involved in attaching and removing this cannot be ignored as the production processes become complex and an increased price is unavoidable.
With method (B) of J.P. No. 63-13233, it is necessary to have the tools and the labor to partially remove the luminescent layer and this complicates the production processes and also inhibits mass production. In particular, when a protection layer of aluminum particles or the like is provided using the luminescent layer as the base, it is necessary to use much labor and special tools such as wire brushes as the removal of the protection layer is difficult.
With method (C) of J.P. No. 62-281229, the portion of the tube where the connection is to be made is connected by blowing out the tubes while the luminescent layer is in place and so the luminescent layer is drawn out when the glass at the connecting portion is made pliant and connected, and so the thickness of the luminescent layer on the inside wall of the connecting portion becomes thinner, and the amount of light emitted is consequently less so that there is an uneven brightness distribution which is not desirable for the external appearance.
Accordingly, fluorescent lamps produced by the above conventional methods are not desirable as they have the problems of reliability, performance and maintenance of the external appearance.